A FTIR and SEM study of PS radiation grafted fluoropolymers:: influence of the nature of the ionizing radiation on the film structure

This study deals with the structure of polymeric films obtained by radiation grafting of polystyrene (PS) in poly(vinylidene fluoride) (PVDF) and poly(vinylidene fluoride/hexafluoropropylene) P(VDF/HFP). These fluoropolymers differ by the small HFP amount present in the copolymer, which plasticizes PVDF and favors the chain mobility. Peroxide grafting kinetic results obtained according to different parameters such as the irradiation type (swift heavy ions and gamma-rays), the absorbed dose, the grafting time and the substrate nature are presented. The lowest absorbed dose is 10 kGy, which is enough to initiate significant grafting. Fourier Transform IR, transmission and Internal Reflection Spectroscopy are used to calculate the PS grafting yields at different depths. In the case of PVDF only, a PS gradient in the thickness is observed which is higher in the case of a gamma-rays initiation than in that of a swift heavy ions one. This might be explained by the fact that the PS diffusion is accelerated in the latent tracks formed after the heavy ions irradiation. Whatever the radiation type, the grafting yield is higher in PVDF than in its copolymer, which is due to the difference of crystallinity. The PS layer formation is observed by Scanning Electron Microscopy. At small grafting yields, the PVDF spherulites are covered with a network of PS that tends to form a continuous layer when increasing the grafting yield; whereas in the case of copolymer, PS seems to penetrate faster in the bulk, so that the formation of the superficial layer is delayed. Our results show that using different kinds of ionizing radiations induces differences in the structure of the grafted films. (C) 1999 Elsevier Science B.V. All rights reserved.